U.S. patent application number 11/447583 was filed with the patent office on 2007-12-06 for arrangement for and method of projecting an image with pixel mapping.
Invention is credited to Daniel Borges DeLazari, Richard Rizza, Michael Slutsky, Askold Strat, Dmitriy Yavid.
Application Number | 20070279722 11/447583 |
Document ID | / |
Family ID | 38789749 |
Filed Date | 2007-12-06 |
United States Patent
Application |
20070279722 |
Kind Code |
A1 |
Yavid; Dmitriy ; et
al. |
December 6, 2007 |
Arrangement for and method of projecting an image with pixel
mapping
Abstract
A laser beam is swept by a scan mirror as a pattern of scan
lines on a projection surface. The scan mirror moves at a variable
speed along each scan line. Each scan line has a number of pixels.
The pixels have time durations proportional to the variable speed
of the scan mirror. A profile memory stores the time durations of
the pixels. A controller causes selected pixels arranged along each
scan line to be illuminated for the time durations stored by the
profile memory to produce an image of uniform brightness and of
uniformly sized pixels and in color.
Inventors: |
Yavid; Dmitriy; (Stony
Brook, NY) ; Rizza; Richard; (N Bellmore, NY)
; DeLazari; Daniel Borges; (Ribeirao Preto, BR) ;
Slutsky; Michael; (Stony Brook, NY) ; Strat;
Askold; (Sound Beach, NY) |
Correspondence
Address: |
KIRSCHSTEIN, OTTINGER, ISRAEL;& SCHIFFMILLER, P.C.
489 FIFTH AVENUE
NEW YORK
NY
10017
US
|
Family ID: |
38789749 |
Appl. No.: |
11/447583 |
Filed: |
June 6, 2006 |
Current U.S.
Class: |
359/198.1 ;
359/212.1 |
Current CPC
Class: |
G02B 26/105 20130101;
G02B 27/141 20130101; H04N 9/3129 20130101; Y10S 359/90 20130101;
G02B 26/101 20130101 |
Class at
Publication: |
359/212 ;
359/204 |
International
Class: |
G02B 26/08 20060101
G02B026/08 |
Claims
1. An image projection arrangement for projecting a two-dimensional
image on a projection surface, comprising: a) a laser assembly for
generating a laser beam; b) a scanner for sweeping the laser beam
as a pattern of scan lines at a distance from the laser assembly on
the projection surface, the scanner including a scan mirror movable
at a speed that varies along each scan line, each scan line having
a number of pixels, the pixels having respective time durations
proportional to the variable speed of the scan mirror; c) a profile
memory for storing the time durations of the pixels; and d) a
controller operatively connected to the laser assembly, the profile
memory and the scanner, for causing selected pixels along the scan
lines to be illuminated for the time durations stored in the
profile memory, and rendered visible, by the laser beam to produce
the image.
2. The image projection arrangement of claim 1, wherein the laser
assembly includes a plurality of lasers for respectively generating
a plurality of laser beams of different wavelengths, and an optical
assembly for focusing and nearly collinearly arranging the laser
beams to form the laser beam as a composite beam which is directed
to the scan mirror.
3. The image projection arrangement of claim 2, wherein the lasers
include red and blue, semiconductor lasers for respectively
generating red and blue laser beams.
4. The image projection arrangement of claim 3, wherein the lasers
include a diode-pumped YAG laser and an optical frequency doubler
for producing a green laser beam.
5. The image projection arrangement of claim 2, wherein the scan
mirror is operative for sweeping the composite beam along a first
direction at a first scan rate and over a first scan angle, and
wherein the scanner includes another oscillatable scan mirror for
sweeping the composite beam along a second direction substantially
perpendicular to the first direction, and at a second scan rate
different from the first scan rate, and at a second scan angle
different from the first scan angle.
6. The image projection arrangement of claim 5, wherein at least
one of the scan mirrors is oscillated by an inertial drive.
7. The image projection arrangement of claim 1, wherein the
controller includes means for energizing the laser assembly to
illuminate the selected pixels for the time durations stored in the
profile memory, and for deenergizing the laser assembly to
non-illuminate pixels other than the selected pixels.
8. The image projection arrangement of claim 1, and an accumulator
for storing integer and fractional time durations of the
pixels.
9. The image projection arrangement of claim 1, and an inversion
table operatively connected to the accumulator for storing inverted
time durations of the pixels, and for generating a brightness
compensation signal.
10. An image projection arrangement for projecting a
two-dimensional, color image on a projection surface, comprising:
a) a support; b) a laser assembly including red, blue and green
lasers on the support, for respectively emitting a plurality of
red, blue and green laser beams; c) an optical assembly on the
support, for optically focusing and collinearly arranging the laser
beams to form a composite beam; d) a scanner on the support, for
sweeping the composite beam in a pattern of scan lines at a
distance from the support on the projection surface, the scanner
including a scan mirror movable at a speed that varies along each
scan line, each scan line having a number of pixels, the pixels
having respective time durations proportional to the variable speed
of the scan mirror; e) a profile memory for storing the time
durations of the pixels; and f) a controller operatively connected
to the lasers, the profile memory and the scanner, for causing
selected pixels along the scan lines to be illuminated for the time
durations stored in the profile memory, and rendered visible, by
the composite beam to produce the image, the controller being
operative for selecting at least some of the laser beams to
illuminate the selected pixels for the time durations stored in the
profile memory to produce the image with color.
11. The image projection arrangement of claim 10, wherein the scan
mirror is operative for sweeping the composite beam along a first
direction at a first scan rate and over a first scan angle, and
wherein the scanner includes another oscillatable scan mirror for
sweeping the composite beam along a second direction substantially
perpendicular to the first direction, and at a second scan rate
different from the first scan rate, and at a second scan angle
different from the first scan angle.
12. The image projection arrangement of claim 10, and an
accumulator for storing integer and fractional time durations of
the pixels.
13. The image projection arrangement of claim 10, and an inversion
table operatively connected to the accumulator for storing inverted
time durations of the pixels, and for generating a brightness
compensation signal.
14. An image projection arrangement for projecting a
two-dimensional image on a projection surface, comprising: a) laser
means for generating a laser beam; b) scanner means for sweeping
the laser beam as a pattern of scan lines at a distance from the
laser means on the projection surface, the scanner means including
a scan mirror movable at a speed that varies along each scan line,
each scan line having a number of pixels, the pixels having
respective time durations proportional to the variable speed of the
scan mirror; c) profile memory means for storing the time durations
of the pixels; and d) controller means operatively connected to the
laser means, the profile memory means and the scanner means, for
causing selected pixels along the scan lines to be illuminated for
the time durations stored in the profile memory means, and rendered
visible, by the laser beam to produce the image.
15. An image projection module for projecting a two-dimensional
image on a projection surface, comprising: a) a support; b) a laser
assembly on the support, for generating a laser beam; c) a scanner
on the support, for sweeping the laser beam as a pattern of scan
lines at a distance from the support on the projection surface, the
scanner including a scan mirror movable at a speed that varies
along each scan line, each scan line having a number of pixels, the
pixels having respective time durations proportional to the
variable speed of the scan mirror; d) a profile memory for storing
the time durations of the pixels; and e) a controller operatively
connected to the laser assembly, the profile memory and the
scanner, for causing selected pixels along the scan lines to be
illuminated for the time durations stored in the profile memory,
and rendered visible, by the laser beam to produce the image.
16. A method of projecting a two-dimensional image on a projection
surface, comprising the steps of: a) generating a laser beam; b)
sweeping the laser beam as a pattern of scan lines on the
projection surface by moving a scan mirror at a speed that varies
along each scan line, each scan line having a number of pixels, the
pixels having respective time durations proportional to the
variable speed of the scan mirror; c) storing the time durations of
the pixels; and d) causing selected pixels along the scan lines to
be illuminated for the stored time durations, and rendered visible,
by the laser beam to produce the image.
17. The image projection method of claim 16, wherein the directing
step is performed by generating a plurality of laser beams of
different wavelengths, and the step of focusing and nearly
collinearly arranging the laser beams to form the laser beam as a
composite beam which is directed to the scan mirror.
18. The image projection method of claim 16, and storing integer
and fractional time durations of the pixels.
19. The image projection method of claim 16, and storing inverted
time durations of the pixels, and generating a brightness
compensation signal.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to projecting a
two-dimensional image of high quality especially in color.
[0003] 2. Description of the Related Art
[0004] It is generally known to project a two-dimensional image on
a projection surface based on a pair of scan mirrors which
oscillate in mutually orthogonal directions to scan a laser beam
over a raster pattern comprised of a plurality of scan lines. The
image is created in the raster pattern by energizing or pulsing a
laser on and off at selected times, thereby illuminating selected
pixels with a beam spot and not illuminating other pixels in each
scan line. The number of distinct beam spots or pixels that can fit
in each scan line is known as the resolution.
[0005] One of the scan mirrors, sometimes referred to herein as an
X-mirror, sweeps the laser beam at a relatively faster speed
generally along a scan direction extending along the horizontal,
and the other of the scan mirrors, sometimes referred to herein as
a Y-mirror, sweeps the scan line at a relatively slower speed
generally perpendicular to the scan direction extending along the
vertical. The X-mirror is oscillated, typically at resonance, at a
scan frequency and at a speed that varies along each scan line.
Thus, the X-mirror has a maximum speed at the center of each scan
line and a minimum speed at the ends of each scan line.
[0006] The variable speed of the X-mirror causes the pixels to have
variable time durations in order to obtain pixels of the same size
on the projection surface. The variable speed of the X-mirror also
causes the pixels to have a variable brightness, that is, the
projected image appears brighter at those pixels where the X-mirror
has a slower speed. These variable time durations and the variable
brightness must be taken into account in order to project the image
with uniformly sized pixels and uniform brightness.
SUMMARY OF THE INVENTION
OBJECTS OF THE INVENTION
[0007] Accordingly, it is a general object of this invention to
provide an image projection arrangement that projects a
two-dimensional image, especially in color, with uniformly sized
pixels and uniform brightness in accordance with the method of this
invention.
[0008] An additional object is to provide a miniature, compact,
lightweight, and portable color image projection module useful in
many instruments of different form factors.
FEATURES OF THE INVENTION
[0009] In keeping with these objects and others, which will become
apparent hereinafter, one feature of this invention resides,
briefly stated, in an image projection arrangement for, and a
method of, projecting a two-dimensional image of high quality,
especially in color. The arrangement includes a laser assembly for
generating a laser beam; a scanner for sweeping the laser beam as a
pattern of scan lines on a projection surface at a distance from
the laser assembly, each scan line having a number of pixels; and a
controller operatively connected to the laser assembly and the
scanner, for causing selected pixels to be illuminated, and
rendered visible, by the laser beam to produce the image.
[0010] In accordance with one aspect of this invention, the scanner
includes a scan mirror, i.e., the X-mirror, movable at a speed that
varies along each scan line. The pixels have respective time
durations proportional to the variable speed of the X-mirror in
order to obtain pixels of the same size on the projection surface.
Hence, to take such variable time durations into account, a profile
memory is provided for storing the time durations of the pixels.
The controller is operatively connected to the profile memory to
cause the selected pixels to be illuminated for the time durations
stored in the profile memory.
[0011] The time durations can be stored only for a single
representative scan line, for example, the center scan line, in
which case, the stored time durations for the representative scan
line are applied to all of the other scan lines; however, this
leads to errors particularly at the upper and lower regions of the
raster scan which are furthest from the center scan line.
Alternatively, the time durations can be stored for all of the scan
lines; however, this requires a multitude of storage locations for
the profile memory. Preferably, to minimize the memory storage
requirement, the time durations are stored for a single scan line,
such as the center scan line, and then only the differences with
the adjacent scan lines are stored in succession for all the scan
lines.
[0012] As discussed above, the brightness of the image varies with
the time durations, that is, the projected image appears brighter
at those pixels where the X-mirror has a slower speed. In further
accordance with this invention, the stored time durations are
inverted (the brightness is inversely related to the time
durations), and the controller generates a brightness compensation
signal. This signal is then multiplied with the incoming video data
to ensure that each pixel has the same brightness.
[0013] In the preferred embodiment, the laser assembly includes a
plurality of lasers for respectively generating a plurality of
laser beams of different wavelengths, for example, red, blue and
green laser beams, and an optical assembly for focusing and nearly
collinearly arranging the laser beams to form the laser beam as a
composite beam which is directed to the scan mirror. The scan
mirror is operative for sweeping the composite beam along a first
direction at a first scan rate and over a first scan angle. Another
oscillatable scan mirror is operative for sweeping the composite
beam along a second direction substantially perpendicular to the
first direction, and at a second scan rate different from the first
scan rate, and at a second scan angle different from the first scan
angle. At least one of the scan mirrors is oscillated by an
inertial drive.
[0014] The controller includes means for energizing the lasers to
illuminate the selected pixels for the time durations stored in the
profile memory, and for deenergizing the lasers to non-illuminate
pixels other than the selected pixels. The controller also includes
means for effectively aligning the laser beams collinearly by
delaying turning on and off the pixels of each of the laser beams
relative to each other.
[0015] The support, lasers, scan mirrors, controller and optical
assembly preferably occupy a volume of about seventy cubic
centimeters, thereby constituting a compact module, which is
interchangeably mountable in housings of different form factors,
including, but not limited to, a pen-shaped, gun-shaped or
flashlight-shaped instrument, a personal digital assistant, a
pendant, a watch, a computer, and, in short, any shape due to its
compact and miniature size. The projected image can be used for
advertising or signage purposes, or for a television or computer
monitor screen, and, in short, for any purpose desiring something
to be displayed.
[0016] The novel features which are considered as characteristic of
the invention are set forth in particular in the appended claims.
The invention itself, however, both as to its construction and its
method of operation, together with additional objects and
advantages thereof, will be best understood from the following
description of specific embodiments when read in connection with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a perspective view of a hand-held instrument
projecting an image at a working distance therefrom;
[0018] FIG. 2 is an enlarged, overhead, perspective view of an
image projection arrangement in accordance with this invention for
installation in the instrument of FIG. 1;
[0019] FIG. 3 is a top plan view of the arrangement of FIG. 2;
[0020] FIG. 4 is a perspective front view of an inertial drive for
use in the arrangement of FIG. 2;
[0021] FIG. 5 is a perspective rear view of the inertial drive of
FIG. 4;
[0022] FIG. 6 is a perspective view of a practical implementation
of the arrangement of FIG. 2;
[0023] FIG. 7 is an electrical schematic block diagram depicting
operation of the arrangement of FIG. 2; and
[0024] FIG. 8 is a schematic block diagram of a pixel mapping
circuit used by the arrangement of FIG. 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Reference numeral 10 in FIG. 1 generally identifies a
hand-held instrument, for example, a personal digital assistant, in
which a lightweight, compact, image projection arrangement 20, as
shown in FIG. 2, is mounted and operative for projecting a
two-dimensional color image on a projection surface at a variable
distance from the instrument. By way of example, an image 18 is
situated within a viewing range of distances relative to the
instrument 10.
[0026] As shown in FIG. 1, the image 18 extends over an optical
horizontal scan angle A extending along the horizontal direction,
and over an optical vertical scan angle B extending along the
vertical direction, of the image. As described below, the image is
comprised of illuminated and non-illuminated pixels on a raster
pattern of scan lines swept by a scanner in the arrangement 20.
[0027] The parallelepiped shape of the instrument 10 represents
just one form factor of a housing in which the arrangement 20 may
be implemented. The instrument can be shaped with many different
form factors, such as a pen, a cellular telephone, a clamshell or a
wristwatch.
[0028] In the preferred embodiment, the arrangement 20 measures
about seventy cubic centimeters in volume. This compact, miniature
size allows the arrangement 20 to be mounted in housings of many
diverse shapes, large or small, portable or stationary, including
some having an on-board display 12, a keypad 14, and a window 16
through which the image is projected.
[0029] Referring to FIGS. 2 and 3, the arrangement 20 includes a
solid-state, preferably a semiconductor laser 22 which, when
energized, emits a bright red laser beam at about 635-655
nanometers. Lens 24 is a bi-aspheric convex lens having a positive
focal length and is operative for collecting virtually all the
energy in the red beam and for producing a diffraction-limited
beam. Lens 26 is a concave lens having a negative focal length.
Lenses 24, 26 are held by non-illustrated respective lens holders
apart on a support (not illustrated in FIG. 2 for clarity) inside
the instrument 10. The lenses 24, 26 shape the red beam profile
over the working distance.
[0030] Another solid-state, semiconductor laser 28 is mounted on
the support and, when energized, emits a diffraction-limited blue
laser beam at about 440 nanometers. Another bi-aspheric convex lens
30 and a concave lens 32 are employed to shape the blue beam
profile in a manner analogous to lenses 24, 26.
[0031] A green laser beam having a wavelength on the order of 532
nanometers is generated not by a semiconductor laser, but instead
by a green module 34 having an infrared diode-pumped, Nd-doped, YAG
crystal laser whose output beam at 1064 nanometers. A non-linear
frequency doubling crystal is included in the infrared laser cavity
between two laser mirrors. Since the infrared laser power inside
the cavity is much larger than the power coupled outside the
cavity, the frequency doubler is more efficient in generating the
double frequency green light inside the cavity. The output mirror
of the laser is reflective to the 1064 nm infrared radiation, and
transmissive to the doubled 532 nm green laser beam. Since the
correct operation of the solid-state laser and frequency doubler
require precise temperature control, a semiconductor device relying
on the Peltier effect is used to control the temperature of the
green laser module. The thermoelectric cooler can either heat or
cool the device depending on the polarity of the applied current. A
thermistor is part of the green laser module in order to monitor
its temperature. The readout from the thermistor is fed to a
controller, which adjusts the control current to the thermoelectric
cooler accordingly.
[0032] As explained below, the lasers are pulsed in operation at
frequencies on the order of 100 MHz. The red and blue semiconductor
lasers 22, 28 can be pulsed directly via the applied drive currents
at such high frequencies, but the currently available green
solid-state lasers cannot. As a result, the green laser beam
exiting the green module 34 is pulsed with an acousto-optical
modulator (AOM) 36 that creates an acoustic traveling wave inside a
crystal for diffracting the green beam. The AOM 36, however,
produces a zero-order, non-diffracted beam 38 and a first-order,
pulsed, diffracted beam 40. The beams 38, 40 diverge from each
other and, in order to separate them to eliminate the undesirable
zero-order beam 38, the beams 38, 40 are routed along a long,
folded path having a folding mirror 42. Alternatively, the AOM can
be used internally to the green laser module to pulse the green
laser beam. Other possible ways to modulate the green laser beam
include electro-absorption modulation, or a Mach-Zender
interferometer. The beams 38, 40 are routed through positive and
negative lenses 44, 46. However, only the diffracted green beam 40
is allowed to impinge upon, and reflect from, the folding mirror
48. The non-diffracted beam 38 may be absorbed by an absorber 50,
preferably mounted on the mirror 48, or can be used for another
useful function.
[0033] The arrangement includes a pair of dichroic filters 52, 54
arranged to make the green, blue and red beams as collinear as
possible before reaching a scanning assembly 60. Filter 52 allows
the green beam 40 to pass therethrough, but the blue beam 56 from
the blue laser 28 is reflected by the interference effect. Filter
54 allows the green and blue beams 40, 56 to pass therethrough, but
the red beam 58 from the red laser 22 is reflected by the
interference effect.
[0034] The nearly collinear beams 40, 56, 58 are directed to, and
reflected off, a stationary fold mirror 62. The scanning assembly
60 includes a first scan mirror 64 oscillatable by an inertial
drive 66 (shown in isolation in FIGS. 4-5) at a first scan rate to
sweep the laser beams reflected off the fold mirror 62 over the
first horizontal scan angle A, and a second scan mirror 68
oscillatable by an electromagnetic drive 70 at a second scan rate
to sweep the laser beams reflected off the first scan mirror 64
over the second vertical scan angle B. In a variant construction,
the scan mirrors 64, 68 can be replaced by a single two-axis
mirror.
[0035] The inertial drive 66 is a high-speed, low electrical
power-consuming component. Details of the inertial drive can be
found in U.S. patent application Ser. No. 10/387,878, filed Mar.
13, 2003, assigned to the same assignee as the instant application,
and incorporated herein by reference thereto. The use of the
inertial drive reduces power consumption of the scanning assembly
60 to less than one watt and, in the case of projecting a color
image, as described below, to less than ten watts.
[0036] The drive 66 includes a movable frame 74 for supporting the
scan mirror 64 by means of a hinge that includes a pair of
collinear hinge portions 76, 78 extending along a hinge axis and
connected between opposite regions of the scan mirror 64 and
opposite regions of the frame. The frame 74 need not surround the
scan mirror 64, as shown.
[0037] The frame, hinge portions and scan mirror are fabricated of
an integral, generally planar, silicon substrate, which is
approximately 150 microns thick. The silicon is etched to form
omega-shaped slots having upper parallel slot sections, lower
parallel slot sections, and U-shaped central slot sections. The
scan mirror 64 preferably has an oval shape and is free to move in
the slot sections. In the preferred embodiment, the dimensions
along the axes of the oval-shaped scan mirror measure 749
microns.times.1600 microns. Each hinge portion measures 27 microns
in width and 1130 microns in length. The frame has a rectangular
shape measuring 3100 microns in width and 4600 microns in
length.
[0038] The inertial drive is mounted on a generally planar, printed
circuit board 80 and is operative for directly moving the frame
and, by inertia, for indirectly oscillating the scan mirror 64
about the hinge axis. One embodiment of the inertial drive includes
a pair of piezoelectric transducers 82, 84 extending
perpendicularly of the board 80 and into contact with spaced apart
portions of the frame 74 at either side of hinge portion 76. An
adhesive may be used to insure a permanent contact between one end
of each transducer and each frame portion. The opposite end of each
transducer projects out of the rear of the board 80 and is
electrically connected by wires 86, 88 to a periodic alternating
voltage source (not shown).
[0039] In use, the periodic signal applies a periodic drive voltage
to each transducer and causes the respective transducer to
alternatingly extend and contract in length. When transducer 82
extends, transducer 84 contracts, and vice versa, thereby
simultaneously pushing and pulling the spaced apart frame portions
and causing the frame to twist about the hinge axis. The drive
voltage has a frequency corresponding to the resonant frequency of
the scan mirror. The scan mirror is moved from its initial rest
position until it also oscillates about the hinge axis at the
resonant frequency. In a preferred embodiment, the frame and the
scan mirror are about 150 microns thick, and the scan mirror has a
high Q factor. A movement on the order of 1 micron by each
transducer can cause oscillation of the scan mirror at scan angles
in excess of 15 degrees.
[0040] Another pair of piezoelectric transducers 90, 92 extends
perpendicularly of the board 80 and into permanent contact with
spaced apart portions of the frame 74 at either side of hinge
portion 78. Transducers 90, 92 serve as feedback devices to monitor
the oscillating movement of the frame and to generate and conduct
electrical feedback signals along wires 94, 96 to a feedback
control circuit (not shown).
[0041] Although light can reflect off an outer surface of the scan
mirror, it is desirable to coat the surface of the mirror 64 with a
specular coating made of gold, silver, aluminum, or a specially
designed highly reflective dielectric coating.
[0042] The electromagnetic drive 70 includes a permanent magnet
jointly mounted on and behind the second scan mirror 68, and an
electromagnetic coil 72 operative for generating a periodic
magnetic field in response to receiving a periodic drive signal.
The coil 72 is adjacent the magnet so that the periodic field
magnetically interacts with the permanent field of the magnet and
causes the magnet and, in turn, the second scan mirror 68 to
oscillate.
[0043] The inertial drive 66 oscillates the scan mirror 64 at a
high speed at a scan rate preferably greater than 5 kHz and, more
particularly, on the order of 18 kHz or more. This high scan rate
is at an inaudible frequency, thereby minimizing noise and
vibration. The electromagnetic drive 70 oscillates the scan mirror
68 at a slower scan rate on the order of 40 Hz which is fast enough
to allow the image to persist on a human eye retina without
excessive flicker.
[0044] The faster mirror 64 sweeps a generally horizontal scan
line, and the slower mirror 68 sweeps the generally horizontal scan
line vertically, thereby creating a raster pattern which is a grid
or sequence of roughly parallel scan lines from which the image is
constructed. Each scan line has a number of pixels. The image
resolution is preferably XGA quality of 1024.times.768 pixels. Over
a limited working range, a high-definition television standard,
denoted 720p, 1270.times.720 pixels, can be obtained. In some
applications, a one-half VGA quality of 320.times.480 pixels, or
one-fourth VGA quality of 320.times.240 pixels, is sufficient. At
minimum, a resolution of 160.times.160 pixels is desired.
[0045] The roles of the mirrors 64, 68 could be reversed so that
mirror 68 is the faster, and mirror 64 is the slower. Mirror 64 can
also be designed to sweep the vertical scan line, in which event,
mirror 68 would sweep the horizontal scan line. Also, the inertial
drive can be used to drive the mirror 68. Indeed, either mirror can
be driven by an electromechanical, electrical, mechanical,
electrostatic, magnetic, or electromagnetic drive.
[0046] The slow-mirror is operated in a constant velocity
sweep-mode during which time the image is displayed. During the
mirror's return, the mirror is swept back into the initial position
at its natural frequency, which is significantly higher. During the
mirror's return trip, the lasers can be powered down in order to
reduce the power consumption of the device.
[0047] FIG. 6 is a practical implementation of the arrangement 20
in the same perspective as that of FIG. 2. The aforementioned
components are mounted on a support, which includes a top cover 100
and a support plate 102. Holders 104, 106, 108, 110, 112
respectively hold folding mirrors 42, 48, filters 52, 54 and fold
mirror 62 in mutual alignment. Each holder has a plurality of
positioning slots for receiving positioning posts stationarily
mounted on the support. Thus, the mirrors and filters are correctly
positioned. As shown, there are three posts, thereby permitting two
angular adjustments and one lateral adjustment. Each holder can be
glued in its final position.
[0048] The image is constructed by selective illumination of the
pixels in one or more of the scan lines. As described below in
greater detail with reference to FIG. 7, a controller 114 causes
selected pixels in the raster pattern to be illuminated, and
rendered visible, by the three laser beams. For example, red, blue
and green power controllers 116, 118, 120 respectively conduct
electrical currents to the red, blue and green lasers 22, 28, 34 to
energize the latter to emit respective light beams at each selected
pixel, and do not conduct electrical currents to the red, blue and
green lasers to deenergize the latter to non-illuminate the other
non-selected pixels. The resulting pattern of illuminated and
non-illuminated pixels comprises the image, which can be any
display of human- or machine-readable information or graphic.
[0049] Referring to FIG. 1, the raster pattern is shown in an
enlarged view. Starting at an end point, the laser beams are swept
by the inertial drive along the generally horizontal direction at
the horizontal scan rate to an opposite end point to form a scan
line. Thereupon, the laser beams are swept by the electromagnetic
drive 70 along the vertical direction at the vertical scan rate to
another end point to form a second scan line. The formation of
successive scan lines proceeds in the same manner.
[0050] The image is created in the raster pattern by energizing or
pulsing the lasers on and off at selected times under control of
the microprocessor 114 or control circuit by operation of the power
controllers 116, 118, 120. The lasers produce visible light and are
turned on only when a pixel in the desired image is desired to be
seen. The color of each pixel is determined by one or more of the
colors of the beams. Any color in the visible light spectrum can be
formed by the selective superimposition of one or more of the red,
blue, and green lasers. The raster pattern is a grid made of
multiple pixels on each line, and of multiple lines. The image is a
bit-map of selected pixels. Every letter or number, any graphical
design or logo, and even machine-readable bar code symbols, can be
formed as a bit-mapped image.
[0051] As shown in FIG. 7, an incoming video signal having vertical
and horizontal synchronization data, as well as pixel and clock
data, is sent to red, blue and green buffers 122, 124, 126 under
control of the microprocessor 114. The storage of one full VGA
frame requires many kilobytes, and it would be desirable to have
enough memory in the buffers for two full frames to enable one
frame to be written, while another frame is being processed and
projected. The buffered data is sent to a formatter 128 under
control of a speed profiler 130 and to red, blue and green look up
tables (LUTs) 132, 134, 136 to correct inherent internal
distortions caused by scanning, as well as geometrical distortions
caused by the angle of the display of the projected image. The
resulting red, blue and green digital signals are converted to red,
blue and green analog signals by digital to analog converters
(DACs) 138, 140, 142. The red and blue analog signals are fed to
red and blue laser drivers (LDs) 144, 146 which are also connected
to the red and blue power controllers 116, 118. The green analog
signal is fed to an acousto-optical module (AOM) radio frequency
(RF) driver 150 and, in turn, to the green laser 34 which is also
connected to a green LD 148 and to the green power controller
120.
[0052] Feedback controls are also shown in FIG. 7, including red,
blue and green photodiode amplifiers 152, 154, 156 connected to
red, blue and green analog-to-digital (A/D) converters 158, 160,
162 and, in turn, to the microprocessor 114. Heat is monitored by a
thermistor amplifier 164 connected to an A/D converter 166 and, in
turn, to the microprocessor.
[0053] The scan mirrors 64, 68 are driven by drivers 168, 170 which
are fed analog drive signals from DACs 172, 174 which are, in turn,
connected to the microprocessor. Feedback amplifiers 176, 178
detect the position of the scan mirrors 64, 68, and are connected
to feedback A/Ds 180, 182 and, in turn, to the microprocessor.
[0054] A power management circuit 184 is operative to minimize
power while allowing fast on-times, preferably by keeping the green
laser on all the time, and by keeping the current of the red and
blue lasers just below the lasing threshold.
[0055] A laser safety shut down circuit 186 is operative to shut
the lasers off if either of the scan mirrors 64, 68 is detected as
being outside of rated values.
[0056] It will be recalled that the inertial drive 66 oscillates
the scan mirror 64 at a resonant frequency whose speed varies along
each scan line. The scan mirror 64 has a maximum speed at the
center of each scan line and a minimum speed at the ends of each
scan line. The variable speed of the scan mirror 64 causes the
pixels to have variable time durations in order to obtain pixels of
the same size on the projection surface. The variable speed of the
scan mirror 64 also causes the pixels to have a variable
brightness, that is, the projected image appears brighter at those
pixels where the scan mirror 64 has a slower speed. These variable
time durations and the variable brightness are taken into account
by a pixel mapping circuit depicted in FIG. 8 in order to project
the image with uniformly sized pixels and uniform brightness.
[0057] As shown in FIG. 8, a clock 200 counts "tics", i.e., time
intervals. The time duration of each pixel is measured by a
plurality of such tics. For example, a pixel in the preferred
embodiment can be measured as having from 3 to about 14 tics, and
up to 16 tics per pixel can be stored for a high degree of
precision. A pixel counter 202 counts the pixels on each scan line,
and a line counter 204 counts the number of scan lines in the image
to be projected. The pixel and line counters 202, 204 are connected
to a profile memory that is advantageously embodied as the look-up
tables 132, 134, 136 of FIG. 7. A master line table 206 is
connected to a current line table 208 and its contents are reloaded
every frame.
[0058] The output of the current line table 208 is connected to an
8-bit accumulator 210 having 4 upper bits for integer storage 212
and 4 upper bits for fractional storage 214, as described below.
The output of the accumulator is inverted in an inversion look-up
table 216 whose output is used for brightness compensation, as
described below.
[0059] The duration of each pixel is not necessarily, and indeed is
often not, an integer number of tics. Typically, the duration of a
pixel is most precisely expressed as a number having a fractional
remainder. One aspect of this invention is that the fractional
remainder of a first pixel is stored in the fractional storage 214
of the accumulator, and is then taken into account for the next
neighboring second pixel. The duration of the neighboring second
pixel is either rounded up or down as the case may be. The contents
of the accumulator after the duration of the second pixel has been
determined are then taken into account for the third and for all
successive pixels on a scan line.
[0060] During a calibration mode, the profile memory is mapped with
the time durations of the pixels. There are various approaches. For
example, the time durations can be stored only for a single
representative scan line, for example, the center scan line, in
which case, the stored time durations for the representative scan
line are applied to all of the other scan lines; however, this
leads to errors particularly at the upper and lower regions of the
raster scan which are furthest from the center scan line.
Alternatively, the time durations can be stored for all of the scan
lines; however, this requires a multitude of storage locations for
the profile memory. Preferably, to minimize the memory storage
requirement, the time durations are stored for a single scan line,
such as the center scan line, and then only the differences with
the adjacent scan lines are stored in succession for all the scan
lines.
[0061] In further accordance with this invention, the stored time
durations from the accumulator 210 are inverted (the brightness is
inversely related to the time durations), and a brightness
compensation signal is generated. This signal is then multiplied
with the incoming video data to ensure that each pixel has the same
brightness. The stored time durations from the accumulator 210 are
not rounded for this purpose since the brightness jumps more
precipitously when rounded time durations are used.
[0062] It will be understood that each of the elements described
above, or two or more together, also may find a useful application
in other types of constructions differing from the types described
above.
[0063] While the invention has been illustrated and described as
embodied in an arrangement for and a method of projecting an image
with pixel mapping, it is not intended to be limited to the details
shown, since various modifications and structural changes may be
made without departing in any way from the spirit of the present
invention.
[0064] Without further analysis, the foregoing will so fully reveal
the gist of the present invention that others can, by applying
current knowledge, readily adapt it for various applications
without omitting features that, from the standpoint of prior art,
fairly constitute essential characteristics of the generic or
specific aspects of this invention and, therefore, such adaptations
should and are intended to be comprehended within the meaning and
range of equivalence of the following claims.
[0065] What is claimed as new and desired to be protected by
Letters Patent is set forth in the appended claims.
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